1. Field of the Invention
The present invention pertains to heart valve prostheses and in particular, to bileaflet heart valve prostheses using pivotable valve members.
2.Description of Related Art
Various types of heart valve prostheses have been proposed, and many give generally satisfactory operation. One popular design for a heart valve prosthesis includes an annular valve body in which a pair of opposed leaflet occluders are pivotally mounted. The occluders are movable between a closed, mated position so as to block blood flow in an upstream direction, thereby minimizing regurgitation, and an open position allowing blood flow in a downstream direction.
Because hemodynamic energy alone is relied upon for proper operation of the heart valve between its open and closed positions, it is generally desirable to reduce friction losses in the heart valve which would needlessly burden the cardiac system. The interfitting occluders and heart valve body, which is typically annular in configuration, are usually designed with a certain amount of "play". A relatively loose fitting engagement between the occluders and the valve body reduces friction losses and is one technique employed to eliminate the possibility of binding of the occluders. Over the countless number of operations of a heart valve, the projections and depressions are subjected to wear. For the reasons set forth in U.S. Pat. No. 4,689,046, spherical projections and depressions are susceptible to significant amounts of "play" in directions lying in the plane of the leaflet and extending generally perpendicular to the diametrical edge thereof. It has been observed that relatively small amounts of wear adjacent the tip of the spherical projection or the corresponding center portion of the recess results in a significant amount of lateral play, even for relatively minute amounts of increased "end play" that is, in directions generally parallel to the diametrical leaflet edge and extending along the hinge points of a leaflet. As a result of this lateral play, the motion and the sequence, especially the synchronous cooperation of the leaflets becomes less well defined. As a result, performance of the leaflet may become erratic, as is evidenced, for example, by an asynchronous closure of the valve. While in general, prior art heart valves have proven to be very reliable, and have in general been shown to have a projected life expectancy exceeding that of the patient, it is desirable to achieve increased margins of safety by providing a prosthesis which substantially exceeds reliability and performance requirements.
Several other improvements to heart valve prostheses are still desired. For example, in order to reduce assembly costs and in order to minimize any difficulties arising from variations in assembly techniques, it is desirable to provide leaflet occluders which may be fitted to the valve body by temporarily distorting the leaflet occluders so as to permit their snap-in engagement within recesses formed in the valve body. Once installed, it is particularly desirable that the leaflet occluders be free to move within the valve body with minimal friction.
In another area of potential improvement, it is desirable to impart a more rapid closing time to the leaflet occluders so as to reduce regurgitation. However, such quickening of the closing time should not be accompanied by an increase in noise during operation of the prosthesis, for example, as the leaflet occluders engage the valve body as they seat thereagainst to block any regurgitation that might otherwise occur.
Also, any rebounding of the leaflets should be controlled so as to prevent any unnecessary wear, and also to conserve hemodynamic energy which operates the prosthesis. In particular, it is important that any decreases in valve closing time do not contribute to rebounding of the leaflets, as might otherwise be expected.
In the past, leaflet occluders have occasionally been slightly undersized so as to allow a purging blood flow therearound, even when the leaflets are closed. Such flows wash over localized, edge surfaces of the leaflets and the valve body to prevent any clotting that might occur at those locations. It is important, however, that hemodynamic energy of a patient be conserved as much as possible and accordingly it is important that the amount of undersizing of the leaflet occluders be accurately controlled. Such sizing, of course, depends upon manufacturing tolerances in the valve body as well as those of the leaflet occluders. Due to concerns with respect to manufacturing costs, which are directly related to manufacturing tolerances, alternative arrangements for providing a purging flow around the leaflet occluders, particularly at their hinged connections to the valve body, in a manner which conserves hemodynamic energy, is still being sought after.